Deposition of a metal oxide catalyst on a carrier



Patented Jan. I, 1952 DEPOSITION OF A METAL OXIDE CATALYST ON A CARRIERLouis E. Malina, Philadelphia, Pa., assignor to Eugene J. Houdry NoDrawing. Application April 21, 1950,

Serial No. 157,413

This invention relates to catalyst manufacture and to improvements incatalytic structure and composition. This application is a continuationin part of my pending application Serial No. 117,500 filed September 23,1949, entitled Cat-alytic Structure and Composition, and which,subsequent to the filing of this application, has been abandoned.

In certain aspects this invention may be considered as an improvement onor further development of the catalytic structures disclosed in apending application of Eugene J. Houdry, Serial No. 95,031, filed May24, 1949, in which active catalytic materials are deposited upon asupport formed of porcelain or an equivalent substance, i. e., a supportwhich, like porcelain, has ,of itself substantially no catalyticactivity but is compact, strong, relatively impervious or of slightporosity, physically resistant, and capable of sustaining temperatureshocks. Upon such a support a base of active alumina (or activemagnesia, beryllia or thoria) is deposited or dispersed as a film, theweight of such film being very small in comparison with the weight ofthe support. Upon the active film or base is deposited a determinedamount of finely dividedcatalyst, such as active catalytic metals ortheir oxides. In order to obtain a firmly adherent film of activealumina, beryllia, magnesia or thoria, a large number of dippings of theporcelain support into an aluminum, beryllium, magnesium or thorium saltsolution was required, each dipping being followed by a heating step todecompose the solution and leave a film deposit on the support. As manyas thirty dippings and successive decompositions. and often more, werenecessary to obtain a. film thickness of the order of .0005 On accountof the extreme thinness of this film deposit great care had to be givento the chemical composition of the porcelain support and to its firing,so that it would be devoid of undesirable components which couldpenetrate the base film and poison either the film or the active metalor metallic oxide catalysts subsequently deposited upon the active basefilm.

It is a principal object of the present invention to develop a procedurewhich will speed up the deposit of a base film on inactive stablesupports.

Another object is to simplify the process of applying a firmly adherentfilm of active alumina, beryllia, magnesia or thoria to a porcelain sup-.port.

9 Claims. (Cl. 252463) so as to prolong the life and improve theeificiency of catalysts. Still other objects and advantages will beapparent from the detailed description which follows.

It has been discovered that a film coating of the order of .001" to.006" can be obtained readily and with a minimum of dipping or sprayingoperations by using a film coating material composed of fine to fairlycoarse particles of the active oxides of alumina, magnesia, beryllia orthoria dispersed thoroughly and uniformly in a salt or other solution ofone of the said metal oxides to form a heterogeneous mixture. Theapplication of the active film coating mixture on inert material such asporcelain is accomplished by dipping to a submerged condition or byspraying. This film coating mixture is applicable to a body of inertmaterial of any size or shape which is to be used for supporting thecatalytic base film and thereon other active catalysts such as thosementioned in the said pending Houdry application Serial No. 95,031.

The film coating, heat treated as hereinafter described, remainsadherent, intact and resists high temperatures, thermal shocks, humidityand any and all changes under such operating conditions as are describedin certain copending applications of Eugene J. Houdry as follows: SerialNo. 783,561 filed November 1, 1947; Serial No. 790,214 filed December 6,1947; Serial No. 790,215 filed December 6, 1947; Serial No. 790,216filedDecember 6, 1947, now U. S. Patent No. 2,552,555, and Serial No. 109,288filed August 9, 1949. A porcelain support plus an active alumina base ofa film thickness of .005" impregnated with platin-um in the proportionof one per cent by weight of the. alumina has been .used as an oxidationcatalyst in an automobile engine and has performed perfectly theequivalent of many thousands of miles of travel without diminution inefliciency.

In order to obtain the proper thickness, strength and adherence of thefilm base to the support it has been found that the amount of thedispersed oxide in the metal salt solution should vary with the porosityof the porcelain support. A higher proportion of powdered oxide isrequired in the heterogeneous mixture when the support is relativelyimpervious or of slight porosity, and a film thickness of the order of.001" to .002" ordinarily results from one dipping in the mixture. Onthe other hand a lower proportion of powdered oxide is required in themixture with low celain supports, but then a film thickness of from.002" to about .005" will ordinarily be obtained with one dipping in themixture. In other words. the quantity of powdered oxide in theoxide-salt solution mixture should vary in inverse ratio with theporosity in porcelain supports of 20 per cent porosity or less porosity.Before use, the powder and liquid solution are thoroughly mixed andground together in a pebble or ball mill for an extended period, such asfrom three to seven hours, to insure the production of a uniformlydispersed mixture.

Ordinarily the mixture comprises one part by weight of active aluminapowder to from two and a half to twelve parts by weight of concentratedor saturated aluminum nitrate solution, since the thickness of the fihnresulting from the use of a given mixture depends upon the porosity ofthe porcelain support and on its. cross sectional area or volume. Thisis understandable from the fact that the nitrate solution alonepenetrates the support, while the fine particles of the alumina powderin the thoroughly ground mixture remain on the surface to form the film.So for a given mixture of powder and solution the film thickness willincrease with increases in porosity of the porcelain; and for porcelainsupports of the same porosity, film thickness will increase withincreases in the volume or cross sectional area of the support.

In its simplest form the process for applying a stable adherent film toinert porcelain supports of slight or low porosity involves thefollowing four distinct steps.

1. The porcelain elements or supports in any size or shape (as disk,cylinder, rod, pellet, etc.) in prefectly clean and dry condition andcompletely free of contaminants are dipped or immersed in, or thoroughlysprayed with, the heterogeneous mixture of active alumina powder andaluminum nitrate solution described above. Time of impregnation, aboutfive minutes, at room temperature.

2. The porcelain elements are then dried for about a half hour at lowtemperatures, as up to about 250 F., followed by a progressive rise intemperature into the range of 800 to 1000 F. for a period of about anhour, after which the heat is shut off and the elements allowed to coolslowly to room temperature in about another hour. The drying may beeffected by hot air or flue gas saturated with steam, or by infraredrays.

3. The porcelain units are then impregnated again with alumina bydipping or immersing them for about five minutes at room temperature instrong or concentrated aluminum nitrate solution which does not containaluminum oxide powder.

4. Drying and heat tempering step, same as step two (2).

The purpose of the third and fourth steps is to harden the filmestablished on the porcelain element or support by the first and secondsteps. In certain instances it has been found advantageous to repeatsteps three and four two or three times in order to obtain the desireddegree of hardness and stability in the film of alumina laid down bysteps one and two. In some instances it has also been advantageous tomake apreliminary dip in the aluminum nitrate solution, in which casethe steps would be taken in this order: (3), (4), (1), (2), (3), (4).While either of the dipping steps may be repeated, it is unusual formore than four dips to be made of any porcelain support, but eachdipping step must be followed by the drying and heat tempering step twoor four. However, all film applying operations should end with stepsthree and four and for most uses the simple four step process of thepreceding paragraph is adequate and satisfactory.

The most frequent variations on the simple four step process of two dipsonly are as follows (omitting mention of the drying and heat temperingstep, two or four which must follow each dipping step) For increasedhardness in the alumina film the dipping steps are (1), (3), (3); or(1). (3). (3), (3); or (3), (1), (3), (3);

For increased thickness of film (1), (1), (3); or (1), (1), (3), (3); or(3), (1), (1), (3); or (1), (1), (3), (3).

The degree of porosity of the insert supports is usually a factor indetermining the number and order of dips, in addition to the use towhich the finished catalyst will be put.

A factor that imposes a practical limit to film thickness of the aluminacoating is that when the film is too thick cracking and flaking of thecoating may occur. However, so far as is now known there is no use towhich the catalyst is subjected requiring a film thickness much greaterthan .005" or .006", and for many uses films o .001, .002" and .003 aresuficient. Films or the latter thicknesses and up to about .006" can beobtained on most lo'w porosity porcelain elements or supports by thesimple four step or two dip process.

While it is preferable to use saturated solutions 0 of aluminum nitratefor both the mixture with powdered alumina and for the film hardeningdips in order to obtain maximum thickness of alumina film under a givenset of conditions, excellent film depositions are obtained when usingunsaturated aluminum nitrate solutions.

A thickness of the active alumina film greater than about .005" can beobtained by repeating the dips (with intermediate drying and heattempering) in the aluminum oxide powder mixture as previously described,the maximum thickness being around .015", but such greater thicknesses,especially above .01", are usually not practical because of a tendencyto flake. Moreover, much thinner than .005" films, such as .001 and evenless, give a product of high utility for many uses.

The salt solution need not be aluminum nitrate. For example, sulphuricacid or aluminum sulphate may be substituted for aluminum nitratesolution for making the oxide powder mixtures of aluminum. Similarlyacids, chlorides and sulphates of beryllium, magnesium and thorium maybe utilized to deposit active films of these materials.

It is to be noted that the porcelain elements or supports to which thealumina film is applied as a base for other catalytic materials have acoefiicient of expansion extremely close to the coefficient of expansionof the alumina film. Accordingly the compact, uniform adherent film,applied in accordance with the present invention, is not dislodged bytemperature shocks and changes. It isolates the inert porcelain supportfrom the oxidizing or other catalytic materials with which the aluminafilm or base is later impregnated to promote the reactions set forth inthe above mentioned copending applications of Eugene J. Houdry. Forexample, by impregnating the base film with platinum, silver, copper,silver-chromium'or copper-chromium or the oxides thereof WEIR I! BUB Ein the proportions indicated in said Houdry application Serial No.95,031, highly efficient catalysts are produced for carrying outoxidizing operations. By impregnating the alumina film with other knownand suitable catalytic materials, catalysts produced in accordance withthe present invention may be employed for hydrocarbon conversionincluding cracking, polymerization, reforming, aromatization, etc., alsofor hydrogenation, and for many other reactions as will be apparent tothose skilled in the art of catalysis.

The principle and the process of operation herein described have beenapplied for depositlng films of active magnesia, beryllia and thoria onporcelain supports with the same success as with alumina. The thin buthighly active film of these materials when formed as herein described onthe catalytically inert porcelain or other equivalent support, ischaracterized by certain very important properties which distinguishfrom the forms of the same elements which are present in the support.For example, the chemical compounds or combinations (A1203, S102, K20,F6203, NazO, etc.) found in porcelain, combine together during thefiring period at 2300 to 3900 F. to produce a complex chemical compoundor chemical compounds in which individual elements lose their identity,are not in finely divided form, and do not possess catalytic activity.On the other hand, the active oxide base or film which is formed on thesupport is a very finely divided material which remains in thiscondition during service and is obtained by precipitation, gelformation, or decomposition of the metal salt or other solution by heatof relatively low temperature. Contrary to the porcelain support, thechemical composition of the active oxide base is not complex: rather,the chemist endeavors to obtain the active base as pure as possible. Forinstance, a commercial activated alumina (catalyst grade) consists ofabout 99.5 per cent pure alumina, the impurities such as iron,manganese, gallium, calcium, sodium, silicon boron, aggregating together0.5 per cent or less.

Another characteristic of active alumina, etc., is the crystallinestructure of this oxide. For example, aluminum hydroxide, precipitatedfrom a salt such as sodium aluminate with hydrochloric acid, when heatedin the range of 800 to 1000 F. becomes the hexaggral crystal oxide, orgamma alumina. If the gamma alumina is then heated in the range of 2100to 2300 F., or higher, it becomes the trigonal crystal oxide, or alphaalumina. Consequently from the crystalline standpoint, a porcelainsupport in which alumina is one of the main constituents, consists ofalumina chemically combined with other constituents in the complexchemical or ceramic material mentioned above and of alumina in alphaform which is catalytically inert. The alumina base formed as a film onthe porcelain support, however, consists of practically pure alumina ingamma form and is a finely divided active oxide and is a part of thecatalyst, whether it promotes, assists the catalytic reaction, orcombines with another metal or oxide in finely divided form,subsequently added, to make a new combination which is the truecatalyst.

The film base is both absorbent and adsorbent, regardless of its degreeof hardness, and hence will securely hold other catalytic material bydeposition and impregnation. On the other hand, the porcelain support isabsorbent only to the exof the'p'orcelain "or equivalent support withthe active base adds the strength and solidity of 'porcelain to thecatalytic qualities of the acti vated alumina or other oxide. However,the combination of porcelain support and active base, although-necessaryfor prolonged life and efficient'operation, does not possess the kindand degree of catalytic activity required for oxidation andotherreactions 'until the active base is impregnated with othercatalytic material, such as finely divided metal or oxide.

What is claimed is:

l. The process of manufacturing a catalyst structure and compositionwhich comprises uniformly dispersing an active metal oxide, selectedfrom the group consisting of the oxides of aluminum, magnesium,beryllium and thorium, in solid finely divided form in a liquid solutionselected from salts of the metals of said group and acids, then applyingsaid mixture to a catalytically inert support and then subjecting thethus coated support to drying and the temperature required to leave onthe support a film of the active metal oxide.

2. The process of manufacturing a catalyst structure and compositionwhich comprises uniformly dispersing active alumina in solid finelydivided form in a liquid solution selected from salts of the groupconsisting of the metals aluminum, magnesium, beryllium and thorium, andacids, then applying said mixture to a catalytically inert support andthen subjecting the thus coated support to drying and the temperaturerequired to leave on the support a film of the active metal oxide.

3. The process defined in claim 1 in which the catalytically inertsupport is of relatively low porosity and in which the said mixture isapplied to the support by immersion of the support in said I mixture.

4. The process defined in claim 1 in which the active metal oxide isdispersed in the said liquid solution by adding the active metal oxidein powdered form to the liquid solution and then grinding, thereby toinsure the production of a uniformly dispersed heterogeneous mixture.

5. The process defined in claim 1 in which the weight of the finelydivided metal oxide relative to the weight of the liquid solution isbetween 1:2.5 and 1:12.

6. The process of manufacturing a catalyst structure and compositionwhich comprises uniformly dispersing active alumina in solid finelydivided form in a solution of aluminum nitrate, then applying themixture to a catalytically inert support and then subjecting the thuscoated support to drying and the temperature required to leave on thesupport a film of the active alumina.

7. The process defined in claim 1 in which the catalytically inertsupport is of low porosity and is immersed in the mixture, and in whichthe coated support after drying and heating is immersed in a saturatedliquid salt solution of a metal of said group and then dried and heattreated to effect decomposition, thus leaving a hardened film on thesupport.

8. The process defined in claim 6 in which the catalytically inertsupport is of low porosity and is immersed in the mixture, and in whichthe coated support after drying and heating is immersed in a solution ofaluminum nitrate and tent or degree of its porosity. The combination Ithen dried and heat treated to efiect decomposi- 2,580,806 '7 tion ofsaid solution, thus leaving a. hardened REFERENCES CITED film on theSupport- The following references are of record inthe 9. The processdefined in claim 1 in which the me of this patent:

base film is impregnated with a finely divided catalytic metal tocombine with the base film and 5 UNITED STATES PATENTS thereby provide acomposition having the re- Number Name Date quired activity foroxidation, the resultant com- 1,939,647 Arnold et a1 Dec. 19, 1933bination constituting a stable catalytic structure. 2,242,627 StricklandMay 20, 1941 LOUIS E. MALINA. 2,487,466 Nahin NOV. 8, 1949

1. THE PROCESS OF MAUNFACTURING A CATALYST STRUCTURE AND COMPOSITIONWHICH COMPRISES UNIFORMLY DISPERING AN ACTIVE METAL OXIDE, SELECTED FROMTHE GROUP CONSISTING OF THE OXIDES OF ALUMINUM, MAGNESIUM, BERYLLIUM ANDTHORIUM, IN SOLID FINELY DIVIDED FORM IN A LIQUID SOLUTION SELECTED FROMSALTS OF THE METALS OF SAID GROUP AND ACIDS, THEN APPLYING SAID MIXTURETO A CATALYTICALLY INERT SUPPORT AND THEN SUBJECTING THE THUS COATEDSUPPORT TO DRYING AND THE TEMPERATURE REQUIRED TO LEAVE ON THE SUPPORT AFILM OF THE ACTIVE METAL OXIDE.